Examples of culinary items used in the context of the present invention include frying pans, sauté pans, pots, woks, crepe pans, Dutch ovens, kettles, casseroles, roasters and grill pans.
Examples of household appliances used in the context of the present invention include deep fryers, skillets or pots for fondue or raclette, and clothing iron soleplates.
Individuals of ordinary skill in the art will know that culinary items must satisfy certain performance criteria in terms of their anti-adhesive properties, scratch resistance and, more generally, their resistance to the various stresses to which they are subjected during use.
Fluoropolymer-based coatings provide the optimal compromise for all these properties. However, some difficulty remains with respect to the adherence of these coatings on the support of the item and numerous solutions have been proposed.
A significant number of the formulations designed to improve the adhesion of polytetrafluoroethylene (PTFE) are achieved using an adhesion co-resin. Heterocyclic polymers, such as polyamide-imides (PAI) and polyimides (PI) are among the most frequently used resins. For use in combination with colloidal dispersions of PTFE, these adhesion co-resins must necessarily be previously dispersed in an aqueous phase.
The starting material is a heterocyclic polymer resin in solution in a polar aprotic solvent such as N-ethylpyrrolidone (NEP) or N-methylpyrrolidone (NMP). Next, salification of the acid groups is achieved via the addition of very basic primary or secondary amines, and then water is introduced into the mixture to effect the phase inversion of the mixture.
It should be noted that most polar aprotic solvents are subject to labeling as a hazardous or even toxic material under the REACH regulation (European Union Regulation concerning the registration, evaluation and authorization of chemical substances as well as the restrictions applicable to these substances). Accordingly, the environmental and health impacts associated with the use of such substances are non-negligible.
Furthermore, the use of salification amines results in the opening of the imide rings of the heterocyclic polymer and accordingly, film formation is often of a lower quality than desired, and the adhesion and/or corrosion-resistance of the obtained coating is weakened. Finally, the use of salification amines, regardless of their type, accentuates yellowing in the development of the coating.
Recently, it has come to light that certain polyphenols found in certain plants and foods (in particular green tea, red wine and cocoa) make it possible to achieve polymerized products that can adhere to different surfaces (Tadas S Sileika et al., “Colorless Multifunctional Coatings Inspired by Polyphenols Found in Tea, Chocolate, and Wine,” Angewandte Chemie International Edition 52(41), 10766-10770 (2013)). Hydrolysable tannins (tannic acid, gallic acid, pyrogallol, epigallocatechin gallate, etc.) present in these food compounds have a chemical structure conducive to adhesion via a chemical reaction of dehydration or chelation with metals or inorganic surfaces.
These polymerized hydrolysable tannins, however, exhibit a rather low thermal resistance that is not compatible with use at high temperatures such as those required, for example, by a culinary item.
Interestingly, it has also come to light that condensed tannins can be used to generate foams that are resistant to high temperatures (greater than 1400° C.) and to the flame of a torch (G. Tondi et al., “Tannin-based carbon foams,” Carbon 47 (2009) 1480-1492).
These tannins are obtained from plants (wood, bark, marc) after simple extraction with water. Condensed tannins thus represent a very interesting resource channel for “green” (i.e. biosourced) primary materials as an alternative to petroleum derivative chemical products.